Carburetors for internal combustion engines, for example motorcycles, show a suction port which is in connection with the combustion chamber of the motor and which is fed with liquid fuel via a nozzle. The suction port is possible to throttle down and to close with a throttle, which is movable between an open position, and a closed position. The throttle may be cylindrical or of a sheet form and be maneuvered with the aid of a wire which is in connection with a so-called throttle twist grip. The nozzle is usually in connection with a fuel channel which leads into the suction port and is opened and closed with the aid of a valve needle which is extending down into the opening of the fuel channel in a direction from the suction port. The valve needle may be rigidly mounted upon the throttle or be in connection with this via a wire. When the suction port is totally open, the valve needle or the wire extends across the suction port.
At motorcycles for racing the motors for cycles in the same racing class are to keep certain measures and dimensions. Also the size of the suction port is limited to a maximum diameter. It has been shown that the motor effect could be increased at a given diameter of the suction port if the placement of the valve needle or the corresponding wire across the suction port could be avoided. The American patent publications U.S. Pat. Nos. 1,793,148 and 4,123,479 described carburetors where the suction openings are not influenced by wires or valve needles but they are not suitable for use with among other things motors for motorcycles for racing.